Transfer bearing for geared turbofan

ABSTRACT

A gear reduction for a gas turbine engine comprises a carrier driven to rotate gears. The gears are supported by journal bearings. The carrier extends through a transfer bearing, which provides oil to passages within the carrier to supply oil to the gears and to the journal bearings. A device limits leakage oil from the transfer bearing to axial ends of the transfer bearing to a controlled amount. A gas turbine engine is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/916,339, filed Dec. 16, 2013.

BACKGROUND OF THE INVENTION

This application relates to a transfer bearing for a gear reduction in ageared turbofan, wherein the oil leakage at axial ends of the bearing iscontrolled.

Gas turbine engines are known and include a fan delivering air into abypass duct as propulsion air and into a core engine, where it flows toa compressor. The air is compressed in the compressor and passesdownstream into a combustor section where it is mixed with fuel andignited. Products of this combustion pass downstream over turbine rotorsdriving them to rotate. The turbine rotors, in turn, drive thecompressor and fan rotors.

Historically, a turbine rotor drove the fan rotor at a single speed.More recently, it has been proposed to include a gear reduction betweena fan drive turbine and the fan rotor.

The gear reductions require adequate lubrication. In one gear reduction,a fan drive shaft is driven by a rotating carrier in a planetary gearsystem. A transfer bearing provides oil to the carrier.

The transfer bearing supplies oil through a plurality of passages in thecarrier, such that oil is supplied to gears and journal bearings withinthe gear reduction.

SUMMARY OF THE INVENTION

In a featured embodiment, a gear reduction for a gas turbine enginecomprises a carrier driven to rotate gears. The gears are supported byjournal bearings. The carrier extends through a transfer bearing, whichprovides oil to passages within the carrier to supply oil to the gearsand to the journal bearings. A device limits leakage oil from thetransfer bearing to axial ends of the transfer bearing to a controlledamount.

In another embodiment according to the previous embodiment, the deviceto limit leakage oil includes a supply of pressurized air to the ends.

In another embodiment according to any of the previous embodiments, thedevice to limit leakage oil includes a labyrinth seal at each axial endof the transfer bearing, with the pressurized air supplied on an opposedside of the labyrinth seal from the axial ends.

In another embodiment according to any of the previous embodiments, thetransfer bearing is static.

In another embodiment according to any of the previous embodiments, thedevice to limit leakage oil also includes piston ring seals.

In another embodiment according to any of the previous embodiments, thedevice to limit leakage oil also includes a carbon gap seal providing acontrolled leakage gap between an inner periphery of the carbon gap sealand an outer periphery of the carrier.

In another embodiment according to any of the previous embodiments, thedevice to limit leakage includes piston ring seals.

In another embodiment according to any of the previous embodiments, thedevice to limit leakage includes a carbon gap seal providing acontrolled leakage gap between an inner periphery of the carbon gap sealand an outer periphery of the carrier.

In another embodiment according to any of the previous embodiments, thetransfer bearing is static.

In another embodiment according to any of the previous embodiments, thegears are planet gears.

In another featured embodiment, a gas turbine engine comprises a fandrive turbine driving a fan rotor through a gear reduction. The gearreduction includes a carrier driven to rotate gears. The gears aresupported by journal bearings. The carrier extends through a transferbearing, which provides oil to passages within the carrier to supply oilto the gears and to the journal bearings. A device limits leakage oilfrom the transfer bearing to axial ends of the transfer bearing to acontrolled amount.

In another embodiment according to the previous embodiment, the deviceto limit leakage oil includes a supply of pressurized air to the ends.

In another embodiment according to any of the previous embodiments, thedevice to limit leakage oil includes a labyrinth seal at each axial endof the transfer bearing.

In another embodiment according to any of the previous embodiments, thetransfer bearing is static.

In another embodiment according to any of the previous embodiments, thedevice to limit leakage oil also includes piston ring seals.

In another embodiment according to any of the previous embodiments, thedevice to limit leakage oil also includes a carbon gap seal providing acontrolled leakage gap between an inner periphery of the carbon gap sealand an outer periphery of the carrier.

In another embodiment according to any of the previous embodiments, thefan drive turbine also drives a compressor, with the gear reductionplaced between the compressor and the fan rotor.

In another embodiment according to any of the previous embodiments, thedevice to limit leakage includes piston ring seals.

In another embodiment according to any of the previous embodiments, thedevice to limit leakage includes a carbon gap seal providing acontrolled leakage gap between an inner periphery of the carbon gap sealand an outer periphery of the carrier.

In another embodiment according to any of the previous embodiments, thetransfer bearing is static.

These and other features may be best understood from the followingdrawings and specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a gas turbine engine.

FIG. 2 shows a portion of a gear reduction.

FIG. 3 is a schematic cross-sectional view.

FIG. 4 is an alternative embodiment.

FIG. 5 is yet another alternative embodiment.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. Alternative engines mightinclude an augmentor section (not shown) among other systems orfeatures. The fan section 22 drives air along a bypass flow path B in abypass duct defined within a nacelle 15, while the compressor section 24drives air along a core flow path C for compression and communicationinto the combustor section 26 then expansion through the turbine section28. Although depicted as a two-spool turbofan gas turbine engine in thedisclosed non-limiting embodiment, it should be understood that theconcepts described herein are not limited to use with two-spoolturbofans as the teachings may be applied to other types of turbineengines including three-spool architectures.

The exemplary engine 20 generally includes a low speed spool 30 and ahigh speed spool 32 mounted for rotation about an engine centrallongitudinal axis A relative to an engine static structure 36 viaseveral bearing systems 38. It should be understood that various bearingsystems 38 at various locations may alternatively or additionally beprovided, and the location of bearing systems 38 may be varied asappropriate to the application.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects a fan 42, a first (or low) pressure compressor 44 and afirst (or low) pressure turbine 46. The inner shaft 40 is connected tothe fan 42 through a speed change mechanism, which in exemplary gasturbine engine 20 is illustrated as a geared architecture 48 to drivethe fan 42 at a lower speed than the low speed spool 30. The high speedspool 32 includes an outer shaft 50 that interconnects a second (orhigh) pressure compressor 52 and a second (or high) pressure turbine 54.A combustor 56 is arranged in exemplary gas turbine 20 between the highpressure compressor 52 and the high pressure turbine 54. A mid-turbineframe 57 of the engine static structure 36 is arranged generally betweenthe high pressure turbine 54 and the low pressure turbine 46. Themid-turbine frame 57 further supports bearing systems 38 in the turbinesection 28. The inner shaft 40 and the outer shaft 50 are concentric androtate via bearing systems 38 about the engine central longitudinal axisA which is collinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 57 includes airfoils 59 whichare in the core airflow path C. The turbines 46, 54 rotationally drivethe respective low speed spool 30 and high speed spool 32 in response tothe expansion. It will be appreciated that each of the positions of thefan section 22, compressor section 24, combustor section 26, turbinesection 28, and fan drive gear system 48 may be varied. For example,gear system 48 may be located aft of combustor section 26 or even aft ofturbine section 28, and fan section 22 may be positioned forward or aftof the location of gear system 48.

The engine 20 in one example is a high-bypass geared aircraft engine. Ina further example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than about ten (10), thegeared architecture 48 is an epicyclic gear train, such as a planetarygear system or other gear system, with a gear reduction ratio of greaterthan about 2.3 and the low pressure turbine 46 has a pressure ratio thatis greater than about five. In one disclosed embodiment, the engine 20bypass ratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout five 5:1. Low pressure turbine 46 pressure ratio is pressuremeasured prior to inlet of low pressure turbine 46 as related to thepressure at the outlet of the low pressure turbine 46 prior to anexhaust nozzle. The geared architecture 48 may be an epicycle geartrain, such as a planetary gear system or other gear system, with a gearreduction ratio of greater than about 2.3:1. It should be understood,however, that the above parameters are only exemplary of one embodimentof a geared architecture engine and that the present invention isapplicable to other gas turbine engines including direct driveturbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, withthe engine at its best fuel consumption—also known as “bucket cruiseThrust Specific Fuel Consumption (“TSFC”)”—is the industry standardparameter of lbm of fuel being burned divided by lbf of thrust theengine produces at that minimum point. “Low fan pressure ratio” is thepressure ratio across the fan blade alone, without a Fan Exit Guide Vane(“FEGV”) system. The low fan pressure ratio as disclosed hereinaccording to one non-limiting embodiment is less than about 1.45. “Lowcorrected fan tip speed” is the actual fan tip speed in ft/sec dividedby an industry standard temperature correction of [(Tram ° R)/(518.7°R)]0.5. The “Low corrected fan tip speed” as disclosed herein accordingto one non-limiting embodiment is less than about 1150 ft/second.

FIG. 2 shows a carrier 104 which may be part of the gear reduction 48 ofFIG. 1. The carrier 104 is driven to rotate and, in turn, will drive afan drive shaft. This is shown schematically in FIG. 3 with fan rotor132 being shown driven by the carrier 104.

As known, the carrier 104 is driven to rotate by gears 114 within aplanetary transmission such as shown schematically in FIG. 3. Ring gear115 reacts the torque from gears 114 to an engine static case 99.

As shown in FIG. 2, a transfer bearing 102 surrounds the carrier 104 andprovides oil to various components in the gear reduction 48.

As an example, as shown in FIGS. 2 and 3, oil for journal bearings 118is supplied at 108. Oil for gears 114 is shown being supplied at 111.

FIG. 3 schematically shows the oil 108 being delivered for the journalbearings 118 supporting gears 114 in the gear reduction 48. As shown,this oil passes into a chamber 97 and then a passage 110. The oil passesout of outlets 112 to lubricate journal bearings 118, which supportgears 114. The gears 114 are shown schematically being supplied by oilfrom outlets 116. The outlets 116 are fed by other passages within thecarrier 104 which are not illustrated. These passages are fed fromsupply 111 and chamber 99. A worker of ordinary skill in the art wouldrecognize how to supply oil from the chamber 99 to the outlets 116 byhaving circumferentially secured passages through the carrier 104.

As known, a fan drive turbine, or the low pressure turbine in the FIG. 1embodiment 46, drives the carrier 104. In this embodiment, the gears 114may be planet gears. In addition, as known, there may be a flexiblecoupling between the two.

In this embodiment, an air supply 120 supplies air through passages 122to chambers 91 at axial ends of the transfer bearing 102. The transferbearing 102 does not actually support the carrier 104, but rather servesas an oil supply device and is static.

Also, labyrinth seals 130 are positioned between the air supply passage122 and the ends of the transfer bearing 102. The air supply 120 andpassages are 122 are designed and sized, along with the labyrinth seals130, to control the amount of leakage oil from zero to a defined levelto be used to lubricate additional features. FIG. 4 shows an alternativeembodiment, where piston ring seals 141 leave a gap 140 allowing acontrolled amount of leakage. The piston ring seals may be used alone orin conjunction with buffer air 122 and labyrinth seal 130.

FIG. 5 shows a carbon gap seal 150, wherein a gap 148 with an outerperiphery of the carrier 104 is controlled again to provide a controlledamount of leakage oil. The carbon seal may also be used with and withoutbuffer air 122 and labyrinth seal 130.

Each of the three embodiments is designed such that the amount of oilleaking from the transfer bearing ends is controlled such that it can beused to lubricate additional features but yet is limited enough suchthat an undue amount of oil is not utilized.

Although an embodiment of this invention has been disclosed, a worker ofordinary skill in this art would recognize that certain modificationswould come within the scope of this invention. For that reason, thefollowing claims should be studied to determine the true scope andcontent of this invention.

The invention claimed is:
 1. A gear reduction for a gas turbine enginecomprising: a carrier driven to rotate with gears, said gears beingsupported by journal bearings; said carrier extending through a transferbearing, said transfer bearing providing oil to passages within saidcarrier to supply oil to said gears and to said journal bearings; adevice to limit leakage oil from said transfer bearing to axial ends ofsaid transfer bearing to a controlled, non-zero, amount; and said deviceto limit leakage includes piston ring seals.
 2. The gear reduction asset forth in claim 1, wherein said device to limit leakage oil includesa supply of pressurized air to said ends.
 3. The gear reduction as setforth in claim 2, wherein said device to limit leakage oil includes alabyrinth seal at each axial end of said transfer bearing, with saidpressurized air supplied on an opposed side of said labyrinth seal fromsaid axial ends.
 4. The gear reduction as set forth in claim 3, whereinsaid transfer bearing is static.
 5. The gear reduction as set forth inclaim 1, wherein said transfer bearing is static.
 6. The gear reductionas set forth in claim 1, wherein said gears are planet gears.
 7. A gearreduction for a gas turbine engine comprising: a carrier driven torotate with gears, said gears being supported by journal bearings; saidcarrier extending through a transfer bearing, said transfer bearingproviding oil to passages within said carrier to supply oil to saidgears and to said journal bearings; a device to limit leakage oil fromsaid transfer bearing to axial ends of said transfer bearing to acontrolled, non-zero, amount; and said device to limit leakage includesa carbon gap seal providing a controlled leakage gap between an innerperiphery of said carbon gap seal and an outer periphery of saidcarrier.
 8. A gas turbine engine comprising: a fan drive turbine drivinga fan rotor through a gear reduction; the gear reduction including acarrier driven to rotate with gears, said gears being supported byjournal bearings; and said carrier extending through a transfer bearing,said transfer bearing providing oil to passages within said carrier tosupply oil to said gears and to said journal bearings, and a device tolimit leakage oil from said transfer bearing to axial ends of saidtransfer bearing to a controlled, non-zero, amount; and said device tolimit leakage includes piston ring seals.
 9. The gas turbine engine asset forth in claim 8, wherein said device to limit leakage oil includesa supply of pressurized air to said ends.
 10. The gas turbine engine asset forth in claim 9, wherein said device to limit leakage oil includesa labyrinth seal at each axial end of said transfer bearing.
 11. The gasturbine engine as set forth in claim 10, wherein said transfer bearingis static.
 12. The gas turbine engine set forth in claim 9, wherein saiddevice to limit leakage oil also includes piston ring seals.
 13. The gasturbine engine as set forth in claim 8, wherein the fan drive turbinealso driving a compressor, with said gear reduction being placed betweensaid compressor and said fan rotor.
 14. The gas turbine engine as setforth in claim 8, wherein said transfer bearing is static.
 15. A gasturbine engine comprising: a fan drive turbine driving a fan rotorthrough a gear reduction; the gear reduction including a carrier drivento rotate with gears, said gears being supported by journal bearings;said carrier extending through a transfer bearing, said transfer bearingproviding oil to passages within said carrier to supply oil to saidgears and to said journal bearings, and a device to non-zero, amount;and said device to limit leakage includes a carbon gap seal providing acontrolled leakage gap between an inner periphery of said carbon gapseal and an outer periphery of said carrier.